Disc player with alternating ascending/descending guide devices

ABSTRACT

A disc player includes: a plurality of pickup devices for reading information from a disc and a plurality of guide devices arranged radiately from a center of the disc, each for radially transferring one of the pickup devices. The guide devices are arranged so that each alternate pickup device is raised or lowered toward the inner circumferential portion of the disc.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of application Ser. No. 08/840,494, filed on Apr. 21,1997, now U.S. Pat. No. 5,848,049, which is a division of applicationSer. No. 08/541,621, filed on Oct. 10, 1995, now U.S. Pat. No.5,677,904.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a system for a video program service,so-called Video On Demand (VOD) system, which supplies video programsutilizing a CATV system or the like in response to user's requests, andmore particularly to a technique for obtaining plural reproductionsignals of the same video program simultaneously from a unique videodisc.

2. Description of the Prior Art

There is known a disc reproduction device having an ability to reproducevideo signals from a unique video disc at different times (hereinafterreferred to as "VOD reproduction"). The device of this type is equippedwith a plurality of pickups for reading information and guide bars forsupporting the pickups around a rotary axis of the disc. The device canreproduce a plurality of video signals simultaneously from a unique discwith a single disc rotation mechanism. It is preferable in the VODreproduction that the video programs periodically start withapproximately same time intervals between them. The interval of theprogram starting times is put the following limit:

Limit of time interval=(total reproduction time of the program)/(thenumber of the pickup device). Since the user generally wishes to watchthe video program from the start, he or she needs to wait for the startof the next program. Shortening the time interval of the programscontributes to the reduction of the user's waiting time. In this view,in order to reduce the user's waiting time, it is required to equip theVOD reproduction device with as many pickup devices as possible. Forexample, where a video program requiring two hour reproduction time isreproduced using four pickup devices, the time interval of the startingtime is a half hour (two hours/4 pickups). Namely, the same program isreproduced four times with delay times of a half hour between them.

However, in the above described VOD reproduction device, the physicalshape and the structure of the pickup device put the limitation on thenumber of pickup device to be equipped, and therefore it is difficult toreduce the time interval of the programs beyond a certain extent.Specifically, the known reproduction device is provided with the guidingmechanism of the pickup (e.g., guide bar) on both sides of the pickup toensure the smooth transfer of the pickup in the radial direction of thedisc. Therefore, if the guide bars are arranged closely to each other soas to increase the number of the pickup device, they contact andinterfere with each other in the proximity of the rotary axis of thedisc due to their structural features (this phenomenon is hereinafterreferred to as "interference").

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a disc playercapable of reducing the program waiting time of the user in VODreproduction.

According to one aspect of the present invention, there is provided adisc player including: a plurality of pickup devices for readinginformation from a disc; and a plurality of guide devices having alongitudinal axis for transferring the pickup device, the longitudinalaxis being directed in a direction rotated by a predetermined angle withrespect to a radial direction of the disc.

According to another aspect of the present invention, there is provideda disc player including at least one pickup device, the pickup deviceincluding: a first pickup device movable substantially in a radialdirection of a disc for reading information from the disc; and a secondpickup device movable substantially in the radial direction of the discfor reading information from the disc, the first pickup device and thesecond pickup device being movable in dependently of and in parallelwith each other.

According to still another aspect of the present invention, there isprovided a disc player including: a plurality of pickup devices forreading information from the disc; and a plurality of guide devicesarranged radiately from a center of the disc for transferring the pickupdevice in a radial direction of the disc, the plurality of guide devicesincluding: first guide devices for raising the pickup device at an innercircumferential portion of the disc; and second guide devices forbringing the pickup device down at the inner circumferential portion ofthe disc, the first guide devices and the second guide devices beingarranged alternately in a circumferential direction of the disc.

According to still another aspect of the present invention, there isprovided a disc player including: first pickup devices arranged inalignment with each other in a radial direction of a disc for readinginformation from the disc; second pickup devices arranged in alignmentwith each other in the radial direction of the disc for readinginformation from the disc; and device for moving the first pickupdevices and the second pickup devices in the radial direction of thedisc, the first pickup devices being arranged in parallel with thesecond pickup devices.

The nature, utility, and further features of this invention will be moreclearly apparent from the following detailed description with respect topreferred embodiment of the invention when read in conjunction with theaccompanying drawings briefly described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view illustrating arrangement of the guide bars of thedisc player according to the first embodiment;

FIG. 1B is an explanatory diagram illustrating how the angle of theguide bar shown in FIG. 1A is determined;

FIG. 2 is a plan view roughly illustrating the structure of the discplayer according to the second embodiment;

FIG. 3A is a block diagram illustrating the structure of the pickupshown in FIG. 2;

FIG. 3B is a cross-sectional view of the pickups shown in FIG. 3Aobserved from the rotary axis of the disc;

FIG. 4 is a view illustrating the structure of the disc player accordingto the third embodiment; and

FIG. 5 is a view illustrating the structure of the disc player accordingto the fourth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments of the present invention will be described belowwith reference to the accompanying drawings.

1st Embodiment

FIG. 1A schematically illustrates the positioning of the guide bars inthe disc player 100 of the first embodiment. As shown, the disc player100 is so constructed that, when the disc 100 is set, plural guide barsG₁ -G₁₂ are positioned with a predetermined angle θ₀ with respect to theradial direction of the disc, respectively. With each of the guide bars,a pickup device is provided in a slidable fashion along the guide bar inthe longitudinal direction thereof. In this embodiment, the pickupdevice is of three-beams type which produces a main beam for tracing thetarget track and two sub-beams for tracing the neighboring tracks. It isnoted however that pickup devices of one-beam type may be alternativelyused. As has been mentioned, where the guide bars are arranged in theradial direction of the disc, the pickup devices probably interfere witheach other due to their physical structures when tracing the innercircumferential portion of the disc simultaneously. However, accordingto the arrangement shown in FIG. 1A, the pickup devices do notphysically and structurally interfere with each other in the vicinity ofthe rotary axis even when most of them trace the inner circumferentialportion of the disc at the same time. Therefore, more pickup devices andguide bars may be equipped on the disc player.

In the case where the pickup device moves along the guide bar in thedirection of the angle θ₀ rotated with respect to the radial directionof the disc, the sub-beams of the three spot type pickup device fail tocorrectly trace the neighboring tracks. This will be explained byreferring to FIG. 1B. FIG. 1B schematically shows the positions of thethree light spots tracing the tracks T₁ -T₃. When the guide bar isarranged in the radial direction of the disc, like the guide bar g, thethree light spots b₀, b₊ and b₋ are positioned as illustrated in FIG.1B. Namely, when the main beam b₀ is tracing the center track T₂, thesub-beams b₊ and b₋ trace correctly the neighboring tracks ₁ and T₃,respectively. Here, the angle produced by the direction in which thethree beams are aligned and the direction of the guide bar is θ₁.Namely, according to the normal arrangement of the pickup device, thealignment direction of the three beams and the direction of the guidebar produces a predetermined angle (θ₁ in this case). On the other hand,when the guide bar direction is rotated like the arrangement of thefirst embodiment, the three beams of the pickup device align in thedirection of the broken line in FIG. 1B. The broken line indicates thealignment direction of the three beams when the pickup device ispositioned on the guide bar so that the alignment direction of the beamsand the guide bar direction maintain the angle θ₁. Namely, the sub-beamsare produced off the neighboring tracks T₁ and T₃ because the alignmentdirection of the three beams has the angle θ₁ with respect to the guidebar direction. As seen from FIG. 1B, the sub-beams cannot trace theneighboring tracks accurately if the first embodiment is simply appliedto the disc player of the three beams type pickup device. For thisreason, in this embodiment, the alignment direction of the three beamsis corrected so that the angle of the tangential direction of the discand the direction of the guide bar, which varies according to thedistance from the disc center, is compensated for, or alternatively thepitch between the main beam and the sub-beams are adjusted, therebycorrectly positioning the three spots B₀, B₊ and B₋ on the tracks T₁-T₃.

Next, the manner of the above correction will be described. Where theguide bar is inclined with respect to the radial direction of the disc,the angle produced by the direction of the guide bar and the tangentialdirection of the concentric circle of the disc gradually variesdependently upon the distance from the disc center, and thereby thetracking control of the sub-beams is made unstable. Now, in FIG. 1B, thetrack pitch of the disc DC is represented by d_(t), the angle producedby the direction of the guide bar G and the tangential direction of thedisc is represented by θ_(r), the angle produced by the direction of theguide bar G and the alignment direction of the three beams isrepresented by θ₂, the pitch between the main beam and the sub beamswhere the guide bar is in the radial direction of the disc isrepresented by d₁, and the pitch between the main beam and the sub-beamsaccording to this embodiment is represented by d₂. In this case, thefollowing equation stands:

    d.sub.2 ·cos (θ.sub.0 +θ.sub.2)=d.sub.1 ·cos θ.sub.1 =d.sub.t                                    (1)

When the guide bar is directed in the radial direction, since the angleθ₁ produced by the direction of the guide bar g and the alignmentdirection of the beams is constant, the pitch d₁ between the main beamand the sub beams is constant. On the other hand, according to thisembodiment, the pitch d₂ and the angle θ₂ vary dependently upon thedistance of the main beam from the disc center. Now, assuming that theradius of the track T₂ from the disc center O is r where the guide bar Ghaving the inclination θ₀ with respect to the disc radial directionpasses the point remote from the disc center O by the distance r₀, thefollowing equation stands: ##EQU1## Therefore, from the equations (1)and (2), the following relationship is obtained: ##EQU2## In theequation (3), the first term is a constant, and r₀ is a fixed value.Accordingly, if the position of the main beam is detected and thedistance r from the disc center is given, the angle θ₂ may be obtained.Then, by controlling the pickup device so that the angle between thealignment direction of the beams and the direction of the guide barmaintains the angle θ₂ thus obtained, the sub-beams trace the tracks T₁and T₃ stably and correctly.

Reversely, in the case where the angle θ₂ between the guide bardirection and the beam alignment direction is kept constant, the pitchd₂ between the main beam and the sub-beams is calculated by thefollowing equation: ##EQU3## and the pitch between the sub-beams may becontrolled. Consequently, in order to correctly position the sub-beamson the neighboring tracks, the pickup device is so controlled as torotate the alignment direction of the three beams according to theequation (3), or alternative means for adjusting the pitch of the beamsis provided.

According to the equations (3) and (4), the value θ₂ or d₂ is obtainedwhen the address of the track where the main beam is tracing isdetected. Therefore, a function table may be prepared and stored in aROM, and the controller of the disc player reads the table to rotate thebeam alignment direction or to adjust the pitch of the beams.Alternatively, if a cam mechanism is provided on the guide bar so thatthe beam alignment direction of the pickup device automatically rotatesaccording to the movement of the pickup along the guide bar, the controlmay be simplified.

As described above, according to the first embodiment, since the guidebar is inclined with respect to the radial direction of the disc, theinterference between the pickup devices in the vicinity of the disccenter may be avoided even when the number of the pickup is increased.As a result, an identical video program on a disc may be reproduced bythe plural pickup devices with a short delay time and hence the waitingtime of the user may be reduced in the VOD reproduction. Further, evenin use of the three-beams type pickup, the alignment direction or thepitch of the beams may be appropriately controlled based on theabove-mentioned equations when the distance of the light beam from thedisc center is detected, thereby the accurate-tracking control may beensured.

2nd Embodiment

Next, the second embodiment of the present invention will be described.FIG. 2 illustrates the structure of the disc player according to thesecond embodiment. As illustrated, the disc player 101 according to thesecond embodiment includes pickup devices 1 for reading information fromthe disc CD and processing units 5 for processing the read-out lightbeams from the pickup devices 1 to convert them into electricalreproduction signals. FIGS. 3A and 3B illustrate the details of thepickup device 1. FIG. 3A is a plan view observed from the upside of thedisc CD, and FIG. 3B is a view observed from the direction X shown inFIG. 3A. As shown, the pickup device 1 includes a magnet M arranged in amanner that the longitudinal axis is directed in the radial direction ofthe disc, and actuators A₁ and A₂ for carrying out the tracking servocontrol and the focusing servo control. Each of the actuators A₁ and A₂includes an object lens L₁ and L₂ for reading information from the disc.The actuators A₁ and A₂ are positioned on the opposite sides of thecenter line CL, which passes the disc center and extends in the radialdirection of the disc, and remotely from the center line CL by thepitches a₁ and a₂, respectively. The processing unit 5 includes a mirror10 for changing the direction of the light beam from an optical system11 and the read-out light beam from the actuator A₁ in the directionperpendicular to the optical path thereof, a mirror 12 for changing thedirection of the light beam from an optical system 13 and the read-outlight beam from the actuator A₂ in the direction perpendicular to theoptical path thereof, and the optical systems 11 and 13 include aphoto-detecting element. FIG. 3B is a view from the central axis of thedisc CD (direction X in FIG. 3A). As shown in FIG. 3B, the actuator A₁includes an objective lens L₁, a frame F₁, a yoke Y₁ housed in the frameF₁ for producing a magnetic field, and a coil C₁ coupled to theobjective lens L₁ for the tracking servo and focusing servo. Similarly,the actuator A₂ includes an objective lens L₂, a frame F₂, a yoke Y₂ anda coil C₂. Between the frames F₁ and F₂, the magnet M having alongitudinal axis directed in the radial direction of the disc isinterposed.

Next, the operation will be described. The disc player 101 drives theactuators A₁ and A₂ independently of each other. The optical systememits a light beam and the mirror 10 reflects the light beam to thedirection of the actuator A₁. The lens L₁ of the actuator A₁ receivesthe light beam and focuses it on the target track of the disc. Theread-out light beam from the actuator A₁ is directed and supplied to theprocessing system 11 by the function of the mirror 10. In the similarmanner, the light beam from the optical system 13 is irradiated on thedisc and the read-out light beam from the actuator A₂ is directed andsupplied to the processing system 13 by the function of the mirror 12.Normally, an actuator includes a coil interposed between two magnets,and the servo control is performed by flowing a current in the coil,i.e., utilizing the magnetic field produced by the two magnets, therebymoving the object lens for the focus servo control. In this embodiment,the magnet M is used by the actuators A₁ and A₂ in common. Namely, thecurrent flows through the coil C₁ within the magnetic field produced bythe yoke Y₁ and the magnet M, thereby performing servo control of theactuator A₁. Similarly, the servo control of the actuator A₂ isperformed by flowing the current through the coil C₂ within the magneticfield produced by the yoke Y₂ and the magnet M.

In this embodiment, two actuators A₁ and A₂ are arranged in a singlepickup device, and the actuators A₁ and A₂ are positioned remotely fromthe center line CL by the pitches a₁ and a₂, respectively. However, ifthe transfer direction of the pickup deviates from the center line CLtoo much, the positions and angles of the main beam and the sub-beamsshould be adjusted, as described in the first embodiment. Therefore, itis preferable that the pitches a₁ and a₂ are as small as possible. Inthis regard, if the pitches a₁ and a₂ cannot be reduced, the positionsand angles of the beams may be adjusted in the same manner as describedin the first embodiment.

As described above, according to the second embodiment, since twoactuators are arranged in a single pickup device, eight programs can besimultaneously reproduced using four guide bars, thereby doubling thenumber of reproduced programs and halving the waiting time.

3rd Embodiment

FIG. 4 illustrates a structure of the disc player according to the thirdembodiment. In FIG. 4, the positional relationship of the guide bars andthe disc is depicted. The disc player 102 includes guide bars GB₁ -GB₈arranged radiately from the disc center O, pickup devices Pu₁ -Pu₈slidable on the guide bars GB₁ -GB₈, respectively, and a motor 20 forrotating the disc CD. The figure at the top of FIG. 4 is a plan view ofthe disc player viewed from the upside thereof, the figure at the middleof FIG. 4 is a cross-sectional view of the disc player sliced at theline A--A, and the figure at the bottom of FIG. 4 is a cross-sectionalview of the disc player sliced at the line B--B. As shown in FIG. 4,around the disc center, guide bars having different slopes (i.e.,inclination) in contrary direction are provided alternately. The guidebars GB₁, GB₃, GB₅ and GB₇ are so constructed as to gradually descendsas it approaches the circumferential edge of the disc. Namely, as thepickup devices Pu₁, Pu₃, Pu₅ and Pu₇ get far from the disc center, theheight of them get lower and they descends away from the disc. On theother hand, guide bars GB₂, GB₄, GB₆ and GB₈ are so constructed as togradually ascends as it approaches the circumferential edge of the disc.Namely, as the pickup device Pu₂, Pu₄, Pu₆ and Pu₈ move away from thedisc center, the height of them get higher and they get closer to thedisc. The area D in FIG. 4 is an area where the pickup devices wouldphysically interfere with each other if eight guide bars are simplyprovided without the sloped or inclined manner arrangement. However, inthis embodiment, since the positions in height of the pickup deviceschange according to the slopes of the guide bars, the pickup devices orthe edge portions of the guide bars are free from the interference witheach other. Therefore, more guide bars and pickup devices may beequipped.

In operation, the pickup devices Pu₁ -Pu₈ are subjected to the heightservo control which raises or lowers the pickup device as a whole wherethe focus control cannot be completed only by the follow-up operation ofthe object lens by means of the actuator. The height servo has beenirregularly used to compensate for the focus servo control where theactual disc curvature is beyond the predicted degree. In thisembodiment, the height servo control is regularly used. For the heightservo control, the focus error signal may be used like the manner of thefocusing servo control. Specifically, at the beginning of thereproduction, the odd-numbered pickup devices Pu₁, Pu₃, Pu₅ and Pu₇ arecontrolled only by the focus servo control without the height servocontrol near the disc center O. As the pickup device moves toward thedisc circumference, the pickup device gradually descends and getsremoter from the disc. When the distance between the pickup device andthe disc goes beyond the followable range of the focus servo, the heightservo is started to ascend the pickup device upwardly. In this manner,the focus control is stably performed around the edge portion of thedisc. On the other hand, the even-numbered pickup devices Pu₂, Pu₄, Pu₆and Pu₈ are controlled in the manner reverse to the above control.Namely, at the beginning of the reproduction, the height servo isperformed to ascend the pickup upwardly. When the distance between thepickup device and the disc falls within the followable range of thefocus servo, the height servo is terminated and only the focus servo isperformed. In this manner, the focus control is stably performed aroundthe edge portion of the disc.

As described above, according to the disc player of the thirdembodiment, more pickup devices can be employed freely from thestructural interferences by providing the guide bars in the slopedmanner, thereby reducing the waiting time of the user in the VODreproduction.

4th Embodiment

FIG. 5 illustrates the positional relationship of the disc and thelenses of the disc player according to the fourth embodiment. In FIG. 5,only the lenses are illustrated for the sake of simplicity. Asillustrated, the disc player 103 is provided with a plurality ofactuators aligned in the radial direction of the disc. The actuators ofthe objective lenses are moved in the radial direction of the disc CD bythe supporting device 22 which movably supports the actuators of thelenses L₁ -L₉. so that the reproduction area of the neighboringactuators overlap with each other in the radial direction of the disc.Since the actuators are arranged in the zigzag manner in the radialdirection, the neighboring two actuators, e.g., L₁ and L₂, can reproducean identical track simultaneously. The motor 21 rotates the disc CD. Themaximum number of the pickup devices to be provided is limited by theradius of the disc and the effective width of the pickup device. Theoptical systems for processing the read-out light beams of theodd-numbered pickup devices Pu₁, Pu₃, Pu₅ and Pu₇ and the even-numberedpickup devices Pu₂, Pu₄, Pu₆ and Pu₈ are positioned alternately ondifferent sides of the radial direction of the disc, thereby avoidingthe structural interference between the pickup devices and reducing thepitch between the neighboring pickup devices.

Next, the operation of the disc player 103 will be described. First, themotor 21 drives the disc CD, and the disc player starts reproduction ofthe first program on the disc CD. The pickup device L₁ reads the lead-inarea, and then reads out information from the first track. As the trackbeing reproduced moves in the outer direction of the disc, the pickupdevice L₁ moves to outer area in the radial direction of the disc. Whenthe pickup device L₁ enters the area where both the pickup devices L₁and L₂ can reproduce information, the pickup device L₂ startsreproduction of the track which the pickup device L₁ is reading. Then,the synchronization of the reproduction signals obtained by the twopickup devices L₁ and L₂ is checked, and when the synchronization isconfirmed, the servo control of the pickup device L₁ is released. Inthis way, the reproduction of the program is taken over from the pickupdevice L₁ to the pickup deice L₂. Similarly, the reproduction of theprogram is taken over from the pickup device L₂ to L₃, from L₃ to L₄,for eight times in the same manner until the pickup device L₉ completethe reproduction of the program at the outermost portion of the disc.The pickup device which has given the reproduction role to the nextpickup and whose servo control is released can newly start reproductionof the program immediately, and hence nine reproductions can becontinued with predetermined delay times using the nine pickup devicessimultaneously.

As described above, according to the disc player of the fourthembodiment, since the plural pickup devices are provided in alignment inthe radial direction of the disc, the VOD reproduction can be achievedwithout the provision of the driving mechanism for each of the pickupdevice independently.

What is claimed is:
 1. A disc player comprising:a plurality of pickupdevices for reading information from a disc; and a plurality of guidedevices arranged radiately from a center of the disc, each of saidplurality of guide devices for transferring a respective one of saidplurality of pickup devices in a radial direction of the disc, saidplurality of guide devices comprising:first guide devices for raisingrespective ones of said pickup devices at an inner circumferentialportion of the disc; and second guide devices for lowering respectiveones of said pickup devices at the inner circumferential portion of thedisc, said first guide devices and said second guide devices beingarranged alternatingly in a circumferential direction of the disc. 2.The disc player according to claim 1, wherein each of said first guidedevices comprises a first supporting member gradually descending from aninner circumference of the disc to an outer circumference of the discfor supporting a respective one of said pickup devices, and each of saidsecond guide devices comprises a second supporting member graduallyascending from the inner circumference of the disc to the outercircumference of the disc for supporting a respective one of said pickupdevices.
 3. The disc player according to claim 1, wherein each of thefirst guide devices gradually raises the respective one of the pickupdevices according to the radial direction of the pickup device, andwherein each of the second guide devices gradually lowers the respectiveone of the pickup devices according to the radial direction of thepickup device.